The purpose of the study is to determine whether men with obstructive sleep apnea have alterations in GH, LH, and cortisol. The investigators also wish to determine whether successful treatment of sleep apnea with nasal CPAP corrects abnormalities in secretion of these hormones. This study has been completed, the data analyzed and is currently being written. We studied 7 males ranging in age from 29 to 59 with a mean body mass index of 44, range 26 to 65 who had moderate to severe OSA (mean apnea + hypopneas/hr = 60, range 24-144). Subjects were studied in random order after : 1) they had used nasal CPAP for 1 month, and 2) they had discontinued it for 7 days. There was a one-month period of nasal CPAP use between the 2 periods. Subjects had a sham sleep study the first night, and beginning at 8 a.m. the following morning, GH was sampled every 10 minutes for the next 24 hours using a long catheter with a sampling port in the adjacent room so as not to disturb sleep. The second night's sleep was monitored with EEGs, EOGs, submental EMG. Respiration was monitored with thermistors, respiratory inductance vests and oximetry. GH was measured by a highly sensitive new chemiluminescence assay. CPAP, as expected, eliminated apneas and hypopneas, improved saturation, and increased slow wave sleep and slow wave sleep continuity. Nasal CPAP significantly increased GH concentrations during sleep, control mean 0.11ug/L + .058 SD, CPAP mean 0.36 ug/L + 0.2 (p<0.05). GH concentrations were significantly increased in each sleep stage except REM. The increase in GH concentration was largest in stage 4 sleep where GH increased 10 fold. CPAP also increased 24-hour GH concentrations in 6 of 7 subjects, but the differences in all 7 subjects did not reach significance (p=0.11). We conclude that moderate to severe OSA significantly decreases GH concentrations during sleep. It also decreases 24 hour GH concentration in most but not all patients with OSA. COMPUTER ONLY.